Dynamic aspects of regional extreme rainfall events during the southwest monsoon period over the Indian subcontinent

This study investigates the favorable conditions to regional extreme rainfall events (ERE) over the Indian subcontinent in terms of circulation and other meteorological parameters from 1951 to 2015. The large-scale dynamical factors leading to various disastrous ERE that occurred over different regions are investigated before, during and after the ERE. However, the contribution of the different factors is different in different regions. In the southwest coast (SWC), the core of low-level jetstream (LLJ) was weak (similar to 5 m/s) almost six days prior to event and then it increases its speed to more than 18 m s(-1) during the ERE over the SWC. The associated moisture, along with strong orographic updraft, leads to the ERE. Similarly, the northeast regions (NER) exhibits ample moisture, and anomalous vertical velocity along with high moist static energy leads to the ERE. The moisture supply in the SWC regions is mainly from the Arabian Sea, and that in the NER is from the Bay of Bengal. In the case of central India (CI) and north central India (NCI), abnormal enhancement of the specific humidity, updraft, high moist static energy, and strong LLJ leads to ERE. Over CI, the LLJ strengthens more than 18 m s(-1) and thereafter it dissipates to a break like condition within next six days. The ERE events generally occurred during active monsoon season in the SWC and CI regions; however, the ERE is occurred during the break or active break transition period in the NCI and NER. The moisture convergence at the surface level also supports favourable conditions for developing vertical clouds, leading to extreme rainfall events.